It is imperative for the effective diagnosis and treatment of chronic fatigue to develop valid and reliable methods to measure the presence and intensity of fatigue, its effect on function, and identify the patient characteristics which are associated with it. The purpose of this study is to correlate the physiological and psychosocial components of fatigue; and the individuals' perceptions of fatigue with performance. We will also validate a battery of self-administered assessment tools including an exercise evaluation which can be used (together) to characterize fatigue, monitor changes, and facilitate selection of appropriate treatments. This is a descriptive pilot study using a convenience sample of a maximum of 36 adults with diagnoses of Chronic Fatigue Syndrome (CFS), Polymyositis (PM) and Rheumatoid Arthritis (RA); and a complaint of fatigue for at least 6 months. A total of nine evaluations are administered including physiological, psychosocial and performance measures. Information regarding the study was sent to fourteen local CFS patients from NIAID. Seven patients responded, three have been seen, two are scheduled to be seen and two who meet the criteria will be scheduled in the future. Thirty-four charts were reviewed from the rheumatology clinic, fourteen of these patients were evaluated and ten of the fourteen met the study criteria and have been evaluated. Data are not yet analyzed.